1. Field of the Invention
The present invention relates to lighting units with light-emitting diodes intended to receive an A.C. supply voltage. It more specifically relates to circuits for powering such devices.
2. Discussion of the Related Art
For a long time, illumination devices have been formed based on incandescent light bulbs or on fluorescent tubes capable of receiving an A.C. supply voltage, for example, a 220-V mains voltage at 50 Hz. More recently, it has been desired to use light-emitting diodes. Such diodes especially have a long lifetime and a high light output. They however require a power supply circuit capable of receiving the A.C. voltage from the mains.
Conventional circuits operate in linear mode, that is, they provide a D.C. voltage and a power adapted to the electrical characteristics of the diodes. The diodes are then maintained on for the entire duration of each halfwave of the mains voltage. This power supply mode has the disadvantage of decreasing their lifetime. Further, linear power supply circuits generally comprise high-voltage capacitors having the disadvantage of being expensive and bulky.